Hydraulic jar



Jan. 26, 1960 w. N. sU'rLlFF 2,922,626

HYDRAULICJAR Filed March 25, 1957 2 Sheets-Sheet 1 ayA/f /u 5.//74/5:

arrow/Ey W. N. SUTLIFF Jan. 26, 1960 HYDRAULIC JAR 2 Sheets-Sheet 2 Filed March 25, 1957 lsleeve a fairly sloppy t.

HYDRAULIC JAR Wayne N. Sutliif, Bakersfield, Calif.

Application March 25, 1957, Serial No. `648,137 11 claims. (cl. ass- 27) This invention relates to oil well tools known as jars and particularly to such jars which are hydraulically operated.

Like all jars, a hydraulic jar is usually assembled as one element in a string of elements, and just above a fishing tool, which is extended into a well bore to recover a drill bit, drill string section, or some other piece of equipment which has been twisted olf or otherwise lost in the bore and which is termed a fish The jar embodies a hammer and an anvil which have freedom for a limited degree of relative movement, and means for retarding movement of the hammer toward the anvil,

while the supporting drill string or cable is placed under vsubstantial tension, and then releasing the hammer causing it to respond to said tension and strike the anvil a violent blow. This blow is generally in an upward direc tion and is transmitted through the fishing tool to the sh whereby the latter is loosened permitting it to be withdrawn from the well. A repetition of such blows is ordinarily required to achieve this end.

The retarding of the hammer movement in a hydraulic jar is accomplished by confining a body of liquid in a cylinder chamber behind a piston and permitting the liquid to slowly escape as the tension increases in the suspending string, until at a certain point in the movement of the piston, a free escape of the confined liquid is permitted, resulting in the hammer striking the anvil.

yUnited States Patent() A hydraulic jar in common use comprises external and chamber and travelling completely freely through an ad-I` jacent section of said chamber of larger diameter. The anvil is formed by an annular shoulder on the external tube at the large end of the cylinder chamber and the hammer is formed on the internal tube and disposed towards the anvil from the piston.

The piston of said prior jar includes a valve sleeve, which shuts off passage of liquid between the sleeve and the piston during the jarring stroke by axially engaging an annular seat on the internal tube, and dependence isi then placed on the escape of liquid through the space between the piston sleeve and the smaller diameter section of the cylinder chamber to retard the initial travel of the hammer toward the anvil. Itis desired of course that this retarding action be at a vgiven rate consistent with the satisfactory performance of the jar and to determine this rate of retardation, the piston sleeve is made with an external diameter which is enough less than the internal diameter of the cylinder chamber to give the In practice, the amount of clearance provided between'the sleeve and the cylinder` I chamber has not proven a satisfactory means of producing a precise degree of retardation on the telescopic action of the jar during the initial part of the jarring stroke. This is because that during this portion of the v Y stroke, the liquid pressures developed in the jarand\ f jarring operation.

mlthe external tube partially lifted as when beginning a latented Jan. 26, 1960 against which the sleeve operates are transmitted to the space within the sleeve and this pressure tends to expand the sleeve. Owing to the fact that this same liquid under the same pressure is owing from the leading end of the sleeve through the space between the sleeve and the cylinder chamber the pressure applied outwardly from within the sleeve is balanced for most of the length of the sleeve. At the trailing end of the sleeve, however, the film of liquid escaping past the sleeve has access to the low pressure area beyond the trailing end of the sleeve and escapes readily into this area. There being no inward pressure against the trailing end portion of the sleeve which would counterbalance the liquid pressure tending to expand this from inside, the trailing end portion of the sleeve is expanded into contact with the wall of the cylinder to an extent which causes an external set of increased external diameter in the trailing end portion of the sleeve. This reduces the clearance between the sleeve and the cylinder Ichamber and the planned degree of retardation by the escape of liquid through this space. The distortion of the trailing end of the sleeve in the prior art above described so impairs the operation of the jar so as to require it to be removed at intervals and the sleeve refinished to restore the normal clearance between the sleeve and the cylinder chamber.

It is another object of the present invention to provide a hydraulic jar embodying such a sleeve and having means facilitating a'close control of the rate at which the liquid is allowed to by-pass the jar piston, and thus the rate of retardation of the piston travel, without the operation of said means being impaired by the expansion of the sleeve resulting from extremely high fluid pressures applied internally thereto.

The above mentioned prior hydraulic jar also has packing preventing escape of the confined liquid from the anvil end of the chamber and a floating packer between said tubes at the opposite end of said chamber to separate the confined liquid from the well liquid and prevent the development of voids in said chamber. It also has another packing outside the floating packer and a hole in the wall of the outer tube admitting well fluid between said packing and said iioating packer. This hole has the disadvantage of providing access of abrasive particles of substantial size into the space between the jar tubes.

It is a still further object of the present invention to provide a hydraulic jar in which said hole, and its attendant `disadvantage noted, and the fixed packing on the opposite side of said hole from the floating packer are eliminated without impairing the operation of the Jar.

Yet anotherobject is to provide a hydraulic jar Vin which the operating liquid is constantly confined under a static pressure in excess of that of the surrounding atmosphere or well liquid, whereby contamination of the confined operating liquid by well liquid leaking past the packings is virtually impossible.

The manner of accomplishing the foregoing objects as well as further objects and advantages will be made manifest in the following description taken in connection with the accompanying drawings in which Fig. l is a diagrammatic elevational view of a prefered embodiment of the hydraulic jar of the invention suspended on a drill string.

Fig. 2 is an enlarged vertical sectional view taken on the line 2 2 of' Fig. 1 and shows the external tube of said jar in downward position and with the piston sleeve lowered from its seat. j

Fig. 3 is a fragmentary view similar to Fig. 2, showing 'line 6 6 of Fig. 2.

Fig. .7 is an enlarged fragmentary cross sectional detail View taken on the Yline 7-7 of Fig. 2.

Fig. 8 is a fragmentary vertical sectional View illustrating a modified form4 of means for confining the operating liquid under a pressure exceeding that of the well huid.

Fig. 9 is a fragmentary, enlarged, vertical sectional yview of a modiied'form Aof the piston valve sleeve of .the invention.

Referring speciically. to the drawings, the invention is `there shown as embodied in a hydraulic jar 10 with this jar suspended on the lower end of a drill string 11 and `connecting at its lower end to a iishingi'tool 12.

The ja-r 10 may (alternatively) be suspended on a drill cable (not shown) but is more commonly employed in the manner herein disclosed.

The jar 10 includes an external tube 13 which telescopically receives an internal tube 14 to provide a tubu- "lar shaped operating liquid chamber 15 `between said.

tubes. The lower end of said chamber is closed by -a. iixed annular packing 16. Its upper end is closed by a floating annular packing 17, these packings being described in detail later.

Between these packings we .find the chamber 1S has 'three sections 1S, 19 and 25j varying in outside diameter as determined by bore 21 and counterbores 22 Aand 23 respectively, formed in external tube 13.

Bore 21 has a keyway 28 throughout its length, an annular liquid receiving groove29 near its lower end, and ashort threaded counter bore 30 for receiving the xed packing 16. A gland 31 screws into the mouth of said counterbore for compressing the packing 16 and retain- 'ing it in place.

Connecting with the liquid receiving groove 29 is a liilling hole 32 (Figs. Zand 7) having a spring ball check vvalve, 33.

An outer tapered counterbore 34 of hole`32 is` threaded to receive a liquid filling nipple (not shown) or a closure plug 35.

Counterbore 23 has a smaller inside diameter than counterbore 22, is separated by the latter, which is rela- Atively short, Afrom the bore 21, and terminates at the upper end of external tube 13, where it is threaded to Areceive tubular joint 40. This joint connects the jar 10 lwith drill string 11 and has a bore 41 with a counterbore 42 providing an annular shoulder 43.

An air vent 44, normally closed by ya plug 45, is provided in external tube 13 near the upper end of lliquid chamber 15 for a reason to be made clear later.

Internal tube 14 is formed by assembling two tubular elements 46 and 47 by a taper threaded joint 48. .lust 'below this joint, element 46 has a piston sleeve slide ybase 49 whichis approximately square in cross section with rounded corner faces 50 (Fig. 6). yJust below the base 49, element 4.6 provides an annular anvil 55 extending radially beyond faces 50 to a diameter less than counterbore 23 but greater than bore 21 of external tube 13. Below anvil 55, element 46 provides a tubular seciton 56 which slidably extends downward `.through bore 21, with a loose iit, and through packing 16 with a snug iit.

Tubular section 56 has a keyway57 in which a key 58 isrigidly mounted, this key being slidable in keyway .2.8 in bore 21 to prevent relative rotation.between;extern al part of tubular section 56. Tubular section .extends loosely downward through packing gland 31 to connect,

through a tubular joint 59, with iishing tool 12.

Internal tube 14 has a well fluid passage 60 throughout its length which connects similar passages in drill string 11 and iishing tool 12.

Tubular element 47 has an enlarged lower section 65, which is of approximately the same outside diameter as anvil 55, and upper section '6.6 which is of approximately the same outside diameter .as tubular section 56 and which has a loose sliding t with tubular joint bore 41.

Formed on .the lower .end of lower section 65 is a hardened and ground radial piston sleeve seat 67. Slidably mounted on slide base 49 is a piston sleeve 68 (Fig. 4) having a cylindrical fbore `69' which makes a close sliding iit with rounded base corner faces 50 (Fig. 6) and an outer cylindrical face 70 which makes a liquid-tight sliding t with counter-bore 23 when disposed within this.

P istonsleeve 68 has a hardened and ground radial face 7,1 at its `upper end` which makes Va liquid tight iit with seat '67 when'held upwardly thereagainst by liquid pressureas shown in Figs. 3 and 4. An annular recess '72 is formed inthe sleeve 68 by removing material at the juncture of outer cylindrical face 70 and radial face 7 1.

` Radial bleeder ports 73 are formed,'in the upper end portion 74 of sleeve 6,8 opposite recess v72, to allow liquid to pass from vertical passages 75, provided between sleeve 68 and slide base 49 by the polygonal shape of the latter, and the portion of liquid chamber section 20 disposed above sleeve 68 when the latter is located within said section, as shown in'Fig. 3, and is` being Ahydraulically pressed upwardly lagainst radial seat 67. These bleeder portsprefera-bly comprise notchescarefully formed Lin ground face 71 to ,have yaprecise aggregate crosssectional `area which will give exactly the desired rate of ow of liquid through these ports during .ajarring operation.

The close control thus aordedmay also be lattained by leaving face71 unbroken and forming bleeder ports by .boringsmall Adiameter holes l76 in radial planes through upper end portion 74 .of sleeve 681as shown in Fig. 9.

`Thisway of `providing bleeder ports, however, lacks the advantage of the notch-type bleeder ports 73 in these being Washed free of any foreign matter, which might have gained admission thereto, on each returnstroke of kthe jai- 10-in which piston sleeve 68 is hydraulically lowered out of contact with radial sleeve seat 67 as shown `in Fig. 2.

nProvided in the lower end of sleeve 6,8 are deep notches 80 which admit operating liquid from below said sleeve against anvil 55 as inrFig. 2. yShould notchesS() be opposite rounded base faces 5G, grooves 81, at the lower ends of the latter, will connect notches 80 with passages 75.

Floating packing 17 is preferably formed of .ay-metal ring 82 which slideably iits both the counterbore 23` and 'finternal Vtube section 66 and is double grooved both internally and externally to mount twovpairs of O-rings vS3 and 84, the latter providing liquid tight seals between the packing land the external and internal tubes 13 and v14..,at the upper vend of liquid chamber 15.

The `floating packing 17 of the invention includes .a means to place the jar operating liquid in chamber .15 under .a constant pressure .in excess of thatof the well .liquid which may be owing through the drill string 11, jar lfandiishing tool 12. This means preferably comprises acoiled expansion spring 35 slidably iittng within .counterbore .42 and compressed between. shoulder 43 and packingll lAn alternative means for .thisfpurpose is 70 shownA in Fig. 8 and will be described later.

The radial shoulder formed by the juncturejof bore21 andcounterbore`22provides an annular hammer 8,6.

'Operation .Tqfpreparei iar. ,lzforusa the. chamber .15.- must beitllsrl Plugs 35 and 45 (Figs. 2 and 7 are removed and a i pressure nipple from a pump for supplying operating liquid is applied in the place of plug 35 and the liquid is pumped into chamber 15 through ball check valve 33 (Fig. 7). Packing 17 is shifted past air escape port 44 by the increasing air pressure, thus allowing all the air to escape from chamber 15 and indicating to the operator when the chamber is filled with operating liquid when this starts to flow from air escape port 44.

Upon this happening, the pump is stopped, plug 45 is replaced, closing air escape port 44. The pump may, if desired, be restarted to fill chamber 15 to the point where packing 17 is shifted to place spring 85 under any desired degree of compression, although a free space is preferably always left between packing 17 and tubular joint 40 to allow for expansion of the liquid in chamber 15 due to increased temperatures generated by the operavtion of the jar.

"The pump nipple is now removed from connection with check valve 33 and plug 35 is replaced in its counterbore 34.

The hydraulic jar 10 is now charged with operating liquid and is in readiness for a fishing operation in a well Vbore when assembled with other units as shown in Fig. 1. The fishing tool 12 having been manipulated, by means of the drill string 11, to cause it to securely grip a fish to be recovered from the well bore, the jar 10 is operated to deliver one or more jarring upward blows through the fishing tool 12 to the fish. This is accomplished by first lowering the drill string to depress external tube 13 from sleeve 68, and pass downward through passages 75 and Y out through deep notches 80 in the lower end of sleeve L68, into the portion of chamber below said sleeve. There being practically no change in the net volume of chamber 15 due to the movement of external tube 13 in either direction relative to internal tube 14, neither of these movements occasions any change in the position of oating packing 17, relative to external tube 13. When an upward pull is now applied to drill string 11, the friction developed by the liquid tight fit between sleeve `68 and 'counterbore 23 produces upward movement of this sleeve with external tube 13, until upper face 71 of said* sleeve engages radial seat 67.

This 'closes all passage of operating liquid upwardly .past piston sleeve 68 excepting through the bleeder orifices 73. These orifices, having been precision formed to al- ',low operating liquid to by-pass sleeve 68 at exactly the rate required to give the necessary retardation to the upward travel of external tube 13, the operator can apply to the drill string the specific strain in thousands of pounds called for in the jarring operation before the piston freeing chamber section 19 moves upwardly with external tube 13 to where it contains piston sleeve 68.

Thusthe 'drill string11 is under the necessary degree of tension to snap the external tube 13 upwardly, when the sleeve 68 is thus freed, to cause a blow to be delivered by .-the hammer 86 on anvil 55 of exactly the desired magnitude.

Another advantage of the present invention is that this degree of precision is not subject to rapid change through .Wear as very little abrasion of seat 67 and. sleeveface 71 results `fi'oncl contacts between these, and the erosion of orifices 73 caused by passage of operating liquid through these orifices under extremely high pressures,

valthough appreciable, is at a very slow rate.

The floating packing 17 maintains the operating liquid in chamber 15 under a constant pressure in excess of that of the well liquid which has access to the upper end of this packing.

This positively prevents any seepage of well liquid into the operating liquid due to slight flaws developing in the packing 17, or other closures of openings having access to chamber 15.

A modified form of packing 90 which may be substituted for packing 17 and spring 85 is shown in Fig. 8. This packing engages thevlower end of va tubular joint 91 which is substituted for joint 40, and lacks counterbore 42 of the latter, aud is trapped within a shallow counterbore 92 provided in theupper portion of counterbore 23 of external tube 13.

Packing 90 includes a vertically perforated metal ring 93 which slides freely in counterbore 92 and is provided with a lower limit stop by a shoulder 94 formed by said counterbore. Trapped between joint 91 and ring 93 is a tubular section 95 of aerated vulcanized rubber known as Unicel rubber which is sheathed by a coating 96 of soft non-aerated rubber.

A salient feature of Unicel rubber is its being cornpressible, due to the air trapped therein being compressible. Thus, the ring 93 is caused to yield, when operating liquid is forced into chamber 15, causing Unicel rubber tube section 95 to become compressed axlally so as to apply a reactive pressure on said liquid in a similar manner to the packing 17 and spring 85.

The claims are:

l. In a hydraulic well jar, the combination of: telescopically associated external and internal tubes producing a cylindrical tubular shaped chamber therebetween for confining a body of operating liquid; a fixed packing sealing off one end of said chamber; a floating packing sealing off the other end of said chamber, said external tube having, between said fixed packing and said floating packing, in the order stated, a first or piston-freeing section of substantially large inside diameter, and a second or piston-fitting section ofa lesser inside diameter than said first section; a hammer formed on said external tube by the shoulder atv the near end of said first section; an anvil formed on` said internal tube and extending radially therefrom in axial opposition to said hammer, theA outside diameter of said internal tube being reduced adjacent to and inwardly from said anvil to provide a piston sleeve slide base terminating at its inner end in a ground sleeve seat; apiston sleeve vertically slidable on said base between said anvil and said seat, and having a ground end face fitting said seat, said sleeve also having Ya cylindrical outer face making a liquid tight sliding t with said second chamber section when disposed therein, there being liquid passage means between said sleeve and said base for freely conducting operating liquid from one end of (said sleeve to the opposite end thereof, escape orifice means of small compact cross-section being provided to permit the escape of operating liquid from said passage means into said second section of said chamber in a drill string.

2. A combination as inl claim 1 in which said passage means is provided by giving said base substantially the cross section of a-'polygon, with yrounded corners of a diameter slidably fitting the. interiorof said sleeve. y

"27 #3,. In a vvhydraulic well jar, `@the combination of: telescopically associated external andinternal tubesproducinv a cylindrical tubular shaped chamber ,therebetween for confining a ,body of operating liquid; atxed packing sealing one end vof said chamber; a oating packingsealf ing the other end of said chamber, said external tube having, Ybetween said xedpacking andsaid' floating packing, a first or piston-freeing section of substantially large inside diameter, and a second or pistontting section of -a lesser inside diameter than saidfrst section; a ,hammer vformed on said external .tube by a shoulder provided at the near end of said first section; anfanvil formed `on said internal tube, and extending radially therefrom into said trst section in axial opposition to saidhammer, .the outside diameter of said 1internal tube being reduced adjacent ,to `and inwardly from said anvil lrto provide a piston sleeve slide v`base terminating at its inner end yin a lground sleeve seat; :a Apiston- -sleeve .vertically slidable on said base between said anvil and said seat, and having aground end face tittingsaid -seat,-. and. acylindricalouter g face -slidable within 1said `second .chamber section .when disposed therein, .slowleakage by-pass Vmeansbeingprovided allowing operating liquid to by-pass said sleeveat `a slow rate when it is in said secondsection and travelling relatively toward said first section, and rapid by-,pass 'z means allowing a rapid ow of operating liquid pastsaid sleeve when it is in said .second .section and travelling Arelatively in the reverse direction; meansapart ifrom ambient fluid pressures for constantly yieldably urging said floating packing into compressive relation`with saidl operating liquid; and check valve controlled inlet means .for introducing liquidintosaid chamber until the chamber is filled and said yieldable compressing means is lcornpressed by said liquid so as to maintain thellatter under a lpressure exceedingambient lluidpressure. v

4. A combination as in claim 3 in which said iloating packing comprises a packer ringslidably engaging ,said lnternal tube `and said. secondsection of lsaid external tube toy form `a oating seal ,with both said .tubes and -close that end of said liquid chamber, and inwhich .said

yieldable compressing Ymeans comprises an expansive coiled spring,and a shoulder providedinternallyon said external tube, said spring beingfinterposedbetween,said

shoulder and said packer ring. V` i 5. Inra telescopic oil well tool 'thefunctioning ofvwhich depends upon the selectivehydraulic damping lofrelative axial movement between .the telescopic parts thereof in a. glven direction, the combination of: a cylinder; a plston telescopically shiftable in -said cylinder, said piston 4including an inner body and a sleeve, the latter cornprlsing the outer layer of said pistonthe outside ofsaid 4sleeve making a close sliding lit with the inside of. said V`cylinder, and being-free for a substantial degree of axial ,movement relative to said lpiston body; and stopson said `,piston body Afor limiting said relative axial Vmovement between said-sleeve and said piston. body, one of said stops providing a ground seat, therebeing a matching ground face on the corresponding end of saidsleeve .which .engages said seat to make a substantially liquid v tight seal between said sleeve and said piston body ,during' .relative movement between said pistonand cylinderin said given direction, there being relatively small liquid escape passage means of lcompact .cross sectional area provided in said piston allowing liquid in said cylinder .to by-pass said piston, during said .relative`movementin.;

,said direction, at a .slow rate. eiective .to substantially lretard vthe rate ofsaid movementinlszaid direction, there v*also being relativelyr large liquid passage means provided in said piston, and access to whichlissupplied by the `separation of said seat-,and sleeve` fa ce during relative movement between said cylinder and piston-in theopposite direction, said large .,liqnidy passage meanis, when access isrthushad-thereto, allowing `liquid in said; cylinder tobyfpass said pistonrelatively-freely.

6. ln 1.a.te1escopic oil well tool, ithe -functioningof, which of said liquid outwardly past said packing r means; a viioating packing ring disposed within said cylinder and surroundingthe other end lsection of said inner tubularellement and makinga slilable sealing engagement with both said cylinder ,and said section, said ring, on one face thereof, thus cooperating with .the other elements recited to-,complete an enclosed tubular liquid confining chamber Tbetween said two tubular elements and on its outer faee being exposed to ambient fluid; resilient means for bias- .ing said .floating packing ring towards said packing means; and means for introducingliquid into said chamber todill the same andplace said resilient means `under tension,

there being passage means provided in said *.toolly allowingliquid in said chamber to byv-pass said piston ata restricted rate to retarda given relative axial movement between said tubular elements.y Y

7. In a piston sleeve valve mechanism whichidiffer- `entially retards axial travel of a r.piston .in opposite directionsin a cylinder, and is adapted to Operate withsubstantial precision under .very large hydraulic loads,; the

`combinationof: a tubular cylinder a portion'offwhich ,has a given uniform inside diameteriapiston,reciproable axially within-said cylinder, *and `including a bodyele- ,ment and a sleeve element mountedon said body element Afor a substantial degree of axialmovernent relative tosaid v body element, said sleeve having an externaldiameter very `elose to said insidediameter of said portion of said cylinder whereby said sleeve makes a close sliding fit with the inside of said portion of said cylinder; a pair `of stops on said body spaced apart to be engaged respectively by opposite ends of said sleeve to limit axial movement ofsaid sleeve on said body, there being liquid passage means/of substantial lcapacity formed in said piston and axially .co-

extensive with the space between said stops; primary and secondary valve means formed by cooperating surfaces on opposite ends of said sleeve and the stops respectively yalternately engaged thereby upon relative reciprocation between said sleeve and said body, each of said valve' means being open when the otheris closed and vice-versa, each valve means beingclosed by a relative axial ,movement between said cylinder and saidpiston tending to frictionally shift said sleeve towards said valve meansea ch valve means, when open, setting up rfree communication between said passage means and the adjacent free space between said cylinder andsaid piston body, said primary valve means, when closed, shutting ot communicationbetween said passage means and the adjacent free spacein said cylinder excepting for relatively large primary escape orice means provided in said piston to connect said passage means and said .adjacent lfree space when said primary valve is closed thereby allowing therelative movement betweensaidcylinder and piston which causedfsa'id primary valve to close, tocontinue substantially freely, said secondaryvalve means, when closed, likewise yshutting off communication lbetween saidpassage means and the adjacent free space in said cylinder excepting forrelatively compact and minute secondary escape orifice means l. either direction. betweensaid piston andfsaid cylinder being restricted, by the fclose fit between. said'sleeve and-said portion of said cylinder while vsaid-.piston is insaid. portion,

to the ow of liquid through said primary or secondary orice means, depending on whether said primary valve means or said secondary valve means is respectively closed at the time.

8. In a telescopic oil well tool, the functioning of which depends upon a selective hydraulic damping of relative axial movement between the telescopic parts thereof in a given direction, the combination of a cylinder provid-ing a liquid chamber; a piston telescopically shiftable in said cylinder, said piston including an inner body and a sleeve, the latter comprising the outer layer of said piston, the outside of said sleeve making a close sliding iit with the inside of said cylinder, and being free for a substantial degree of axial movement relative to said piston body; and stops on said piston body for limiting said relative axial movement between said sleeve and said piston body, a relatively large axial passage means being provided in said piston and extending between said stops, one end of said passage means being constantly in relatively free communication with the portion of said chamber at that end of said sleeve, annular ground mating faces being provided on the opposite end of said sleeve and the adjacent stop to form a by-pass valve, one of said faces being radially interrupted by at least one very small short groove forming a bleeder port for said valve when the latter is closed by engagement of said faces, movement of said piston axially in a direction causing said valve to close thus effecting a powerful damping action retarding said movement, While reversing the direction of movement of said piston opens said valve permitting free movement of said piston in that direction and exposing said port to the washing action of liquid owing reversely through said opened valve.

9. In a telescopic oil Well tool, the functioning of which depends upon a selective hydraulic damping of relative axial movement between the telescopic parts thereof in a given direction, the combination of: a cylinder providing a liquid chamber; a piston telescopically shiftable in said cylinder, said piston including an inner body and a sleeve, the latter comprising the outer layer of said piston, the outside of said sleeve making a close means being provided in said piston and extending be-v tween said stops, one end of said passage means being constantly in relatively free communication with the portion of said chamber at that end of said sleeve, annular ground mating faces being provided on the opposite end of said sleeve and the adjacent stop to form a by-pass valve, at least one short bleeder port with compact cross sectional area being provided in said piston which radially connects the end of said passage means at said valve with the adjacent portion of said cylinder chamber, said port allowing a restricted flow of liquid from said passage means into said chamber portion when said valve is closed by engagement of said faces, movement of said piston axially in a direction causing said valve to close thus eifecting a powerful damping action retarding said movement, while reversing the direction of movement of said piston opens said valve permitting free movement of said piston in that direction and exposing said port to the washing action of liquid flowing reversely through said opened valve.

10. A combination as in claim 9 in which said bleeder port comprises at least one hole provided in said piston close to and approximately coextensive with the radial dimension of an adjacent one of said ground faces.

11. A combination as in claim 9 in which said bleeder port is lformed in said sleeve.

References Cited in the ile of this patent UNITED STATES PATENTS 2,315,905 Stafford Apr. 6, 1943 2,499,695 Storm Mar. 7, 1950 2,551,868 Brady May 8, 1951 2,645,459 Sutlii Julyy 14, 1953 2,710,171 Bagnall a .-e 11111@ 71 '19,55 

